In the production of core drill bits for boring into hard rock and similarly hard formations, an abrasive grit material is incorporated in to the bit matrix to improve cutting and reduce drill bit wear. This abrasive grit material can be a number of different abrasive particles including diamond grit and synthetic diamond grit.
The remaining portion of the drill bit is often made up of refractory metal powders, the most common being tungsten, and an infiltrant.
In manufacturing the core drill bit, a matrix is first formed by mixing the refractory metal powder and the abrasive grit material, together with a organic binder material, which helps to hold the abrasive grit particles place. The matrix is placed in a mould and a steel tube in placed on top of the mould, onto which the matrix will be alloyed. An infiltrant is then arranged around the steel tube, in such a way that melted infiltrant will run interstitially between the particles of refractory metal powder and abrasive grit material in the mold and promote wetting and adhesion to the steel tube. The entire assembly is then heated to at or above the liquidus temperature of the infiltrant and the infiltrant permeates the assembly and forms a strong and solid alloy around the steel tube.
In choosing a suitable metal powder or refractory metal powder, it is desirable to select one that has a very high melting point and will not melt or deform during furnacing. This is important to ensure that the abrasive grit particles stay exactly where they were placed when the powders are mixed and placed in the mould.
It is further desirable that the matrix achieves fast cutting rates while providing the above high melting point and strength. A number of refractory metal powders have shown promise in the past in this respect.
However, at the high furnacing temperatures required for alloying it is important not to let the metal powder become oxidized in the furnacing process. This is a common problem with a number of different metals that would otherwise be suitable for use in core drill bits for hard rock drilling purposes. Oxidation, or rust, covers the surface of the refractory metal powder and inhibits good adhesion and wetting with the infiltrant. This leads to a weak and poorly alloyed drill bit of compromised strength.
Attempts have been made to inhibit oxidation during the furnacing process. Most commonly, the furnacing atmosphere has been purged of oxygen and filled with hydrogen. Furnacing in a hydrogen environment as opposed to a normal air environment is considerably more costly, both due to the added cost of the hydrogen gas, but also in evacuating the furnacing chamber of air and pumping in hydrogen. As well, hydrogen poses a serious safety concern, due to its extreme flammability. For this reason, it must be pumped out of the chamber after every furnacing, leading to further expense and safety issues.
It is of great value to find and develop refractory metal powders which can be furnace under ambient conditions and achieve desirable fast cutting rates.